Currently EMT is connected by using one of two methods, either a set screw coupling or a compression coupling. The connectors are made from either electroplated steel or from die cast zinc. Set screw EMT couplings are sleeves which slip over the outside diameter of two opposing EMTs. Set screw EMT couplings typically have an inner ridge to make sure that the two pieces of EMT butt up properly to the center of the coupling. The coupling has set screw(s) that penetrate the wall of the coupling and when tightened create both a ground path and a tight fit.
Compression couplings are made of three “body parts” plus a split gland ring. The inner body is threaded on each end and then the split gland ring is slipped on and then the “outer body” on each end is threaded onto the inner body. By tightening the outer body ends, the split gland ring is tightened around the EMT, providing a tight fit and a good ground path.
In the installation of EMT, provisions have to be made to address the need for a good ground path. Concerns have frequently been raised by inspectors and regulators about the integrity of the ground path of steel EMT. The integrity of the ground path may be degraded if the set screws or compression sleeves are not tightened fully because electrical continuity relies on good, tight connections at each connection or coupling point.
Traditional set screw connectors are basically the same as couplings except one end is threaded or has some other type of attaching mechanism so that the EMT can be attached to an enclosure, such as a junction box or some other piece of equipment that has a knock out hole of the correct size for the connector to fit. Connectors are usually held in place with locknuts that lock the connector into place and provide a continued ground path.
Existing EMT couplings and connectors require the installer to either turn a set screw or turn an “outer body.” The need to “tighten” a set screw or “turn” an outer body not only requires additional work space but is also subject to human error, such as inadequate tightening. If threaded connections are subject to vibration, the screws and/or outer bodies can loosen over time, compromising the ground path. Moreover, “twist tightening” increases the time and effort it takes for mechanics to install EMT. Thus, a need exists for an EMT coupling and connector system and method that does not require set screw or other means of twist tightening while still providing a proper ground path.
Currently available snap fit connectors and couplings are expensive to manufacture and provide a less than optimal ground path.